1. Technical Field
The disclosure relates to a method and an arrangement for exhaust gas recirculation (EGR) in an internal combustion engine.
2. Background Art
Methods and arrangements for exhaust gas recirculation have long been used in internal combustion engines to improve efficiency and reduce emissions. In diesel engines in particular, the recirculation of exhaust gas is known for reducing particulate matter and nitrogen oxide emissions.
In an internal combustion engine having a turbocharger, it is possible for exhaust gas to be extracted upstream of the turbine of the turbocharger and to be supplied to the charge air of the engine downstream of the compressor of the turbocharger, in particular downstream of the charge air cooler which is generally connected downstream of said compressor. With this type of EGR, the exhaust-gas circuit is situated in the high-pressure and high-temperature region of the engine, such that usually no exhaust-gas condensate is generated therein. Such high-pressure EGR however has some disadvantages, for example relatively high particulate emissions in the case of diesel engines.
Alternatively, it is known for exhaust gas to be extracted downstream of the turbine of the turbocharger and to be supplied to the inducted charge air upstream of the compressor of the turbocharger. With such low-pressure exhaust-gas recirculation, however, condensate forms on account of the cooling of the recirculated exhaust gas. The condensate contains primarily water with a small concentration of aggressive compounds such as nitric acid, sulfuric acid, and/or sulfurous acid. Furthermore, the condensate contains solid matter in the form of particulates which originate primarily from particulate matter formed in the engine. If the exhaust gas to be recirculated is branched off downstream of an EGR system, which may include inter alia a particulate filter, then the particulate matter in the condensate is reduced. Nevertheless, even in this case, the condensate also contains residual particles and particulate matter from the exhaust system which may for example have become detached, as a result of wear or as a result of chemical or mechanical influences, from the particulate filter or from other components of the EGR system. Herein, the particulate matter is encompassed within the expression “condensate”, even though they at least partially have a different origin and/or a different composition than the liquid or solid exhaust-gas constituents which are generated as a result of condensation or directly in the combustion chamber.
If the condensate, which is entrained in droplet or particle form, in the exhaust gas now passes into the compressor as a result of being added to the charge air taking place upstream of the compressor, the droplets and the particles can damage the compressor blades on account of the very high speeds of the compressor blades.
It is therefore proposed in DE 10 2005 023 958 A1 that the recirculated exhaust gas be conducted through a condensate separator and that the corrosive component of the exhaust gas thereby be removed from the exhaust-gas flow. For the removal of the condensate, a thermal process is provided, as a result of which the acids contained in the condensate are converted into non-harmful gases and water which are added to the main flow of the exhaust gas downstream of the branch of the exhaust gas to be recirculated and which are discharged to the atmosphere via the exhaust tailpipe. The thermal condensate removal takes place in a multi-stage device in which a heating element, at a temperature of up to 450° C., evaporates and/or reacts aggressive substances. This process and apparatus are associated with a comparatively high level of technical expenditure. In the event of insufficient heating, it is not possible to prevent the discharge of harmful acids to the environment.